1. Field of the Invention
The present invention relates to a tape-on-wafer mounting apparatus and method for mounting a dicing tape on a semiconductor wafer (hereinafter simply called a wafer) before the wafer is divided into chips (or diced).
The process for manufacturing semiconductor devices includes a process in which a wafer having a plurality of chip circuits arranged on an entire surface thereof, is divided into a plurality of chips or diced.
When a wafer is diced, a method generally used to prevent chips diced from getting scattered and lost or even damaged due to a collision with each other, is to mount or stick a dicing tape on the entire surface of the wafer's back and then to cut the wafer to a depth where the dicing tape is not cut through. However, as a wafer becomes large-sized, the wafer becomes liable to bend due to its own weight and it becomes difficult to mount the dicing tape uniformly and firmly on the wafer. Accordingly, a dicing tape-on-wafer mounting apparatus and method for mounting a dicing tape on a semiconductor wafer uniformly and firmly on the wafer, is in great demand.
2. Description of the Related Art
FIG. 1 (a)-(c) illustrate a technical background of the present invention, each showing a wafer before dicing, in the process of dicing and after diced, respectively.
In FIG. 1 (a), a round wafer 1 has a plurality of chip elements 11 including chip circuits 11a, arranged on an entire surface (on the top side in the Figure) of the wafer 1. If the wafer 1 is diced into chip elements 11 as it is, the chip elements 11 diced may scatter or collide with each other, causing some of them to be lost or damaged in circuit function.
To prevent this, firstly a dicing tape 12, which is large enough to cover the wafer 1, is mounted (or stuck) on the back (the bottom side in the Figure) of the wafer 1 on which chip circuits 11a are not fabricated, as shown by an arrow. Secondly, the wafer 1 is grooved in a gridiron layout between the chip elements 11 by using a circular saw 13, to the depth of its thickness but where the dicing tape 12 is not cut through, as shown in FIG. 2 (b). The dicing tape 12 is made of polyethylene, for example, and has an adhesive 12a having a property to lose viscosity when irradiated by ultraviolet rays, applied on one side (the top side of the tape in the Figure).
Since the chip elements 11 diced are stuck to the dicing tape 12 as they are arranged in order as shown in FIG. 1 (c), they will never scatter or collide with each other, which facilitates reservation and transfer of them. Accordingly, the chip elements 11 diced can easily be peeled off and separated from the dicing tape 12 by irradiating ultraviolet rays on the entire surface of the wafer 1, as required.
FIG. 2 (a)-(b) show an example of a conventional dicing tape-on-wafer mounting apparatus and method. FIG. 2 (a) is a schematic sectional view of a dicing tape-on-wafer mounting apparatus 2, taken along a line passing the center of a wafer 1. FIG. 2 (b) is a sectional view of the dicing tape-on-wafer mounting apparatus 2, with a dicing tape 12 being stuck to the wafer 1.
In FIG. 2 (a), the dicing tape-on-wafer mounting apparatus 2 consists mainly of a wafer stage 21, a tape stage 22 and a roller 23. The tape stage 22, which has a flat and ring-shaped dicing frame 22a on its top surface for mounting the dicing tape 12, is coupled to a chamber (not shown) and moves up and down with respect to the wafer stage 21 in a fashion that it encloses the wafer stage 21. The roller 23 moves while rotating on the top surface of the tape stage 22, along a diameter of the tape stage 22.
The wafer stage 21 has a truncated cone-shaped recess (or hole) 21a on its top surface for mounting the wafer 1 therein. The recess 21a is constructed such that the diameters of its upper and lower bases are larger and smaller than that of the wafer 1, respectively and, when the wafer 1 is put in the recess 21a, the top surface of the wafer 1 stands higher than the top surface of the wafer stage 21.
The surface of the roller 23 is made of an elastic member (e.g., silicone rubber) and its length is made larger than the diameter of the wafer 1.
Thus, when the wafer 1 is mounted in the recess 21a coaxially (with the center of the wafer 1 aligned) with the recess 21a, with the wafer surface 1a having the chip circuits 11a fabricated thereon, faced down, the wafer back (shown upward in the Figure) of the wafer 1 comes slightly higher than the top edge 21b of the wafer stage 21.
Next, when the dicing tape 12 is mounted and stuck on the dicing frame 22a via the adhesive 12a while the dicing tape 12 is being pulled with a jig (not shown) to give tension thereto and, as the tape stage 22 is lowered gradually, the dicing tape 12 is mounted onto the wafer back 1b which stands out slightly above the top edge 21b of the wafer stage 21 (see FIG. 2 (b)). Then, when the roller 23 is rolled along the arrow B, the dicing tape 12 is pressed and stuck on the wafer back 1b. Thus, the wafer 1 with the dicing tape 12 stuck thereon is obtained by cutting off the part of the dicing tape 12 protruding the circumference of the wafer 1.
The above-mentioned method is useful in sticking a tape onto a wafer closely when the wafer is flat. However, the latest trend is toward a large-sized and thin wafer in order to improve productivity of semiconductor chips by fabricating as many chips as possible on a larger wafer and to meet the demand for small-sized chips.
Since the wafer 1 is held with the circumference edge of the wafer surface 1a which has chip circuits 11a fabricated, laid on the wafer stage 21, the wafer 1 tends to cave and hang down at its center portion as it becomes larger and thinner. Even if the roller 23 is pressed onto the dicing tape 12 with the wafer 1 at this state, the dicing tape 12 will fail to contact the wafer 1 closely and develop a gap at the center portion, collecting air there and preventing the dicing tape 12 from sticking uniformly and firmly on the wafer back 1b.
Therefore, a problem is that chip elements 11 diced in the dicing process peel off and scatter easily, causing some of them to be lost or damaged due to a collision and, eventually decreasing the productivity of semiconductor devices.